The present invention broadly relates to vehicle guidance systems and, more specifically, pertains to a new and improved passive track system for robotic transport and assembly devices.
Generally speaking, the present invention relates to a passive track system for guiding and controlling robotic or driverless transport and assembly devices, especially floor-level industrial trucks or conveyances, comprising a passive track serving as a control line or guide marker applied to the floor and having at least one characteristic differentiating it from the remaining travel lane, as well as a vehicle-supported sensing or scanning device for following the passive track.
In other words, the passive track guidance and control system of the present invention is for use on a traffic surface for robotic vehicles and comprises a passive track applied to the traffic surface as a guide marker for guiding the robotic vehicles. The traffic surface has at least one identifying characteristic and the passive track has a centerline and exhibits at least one identifying characteristic optically distinguishable from the at least one identifying characteristic of the traffic surface. An optical sensing device is mounted on each vehicle of the robotic vehicles for optically tracking the passive track.
The method of the present invention is for operating a passive track guidance and control system on a traffic surface for robotic vehicles and comprises the steps of employing an optical sensing device mounted on at least one vehicle of the robotic vehicles and comprising a plurality of track sensors to monitor a passive track applied to the traffic surface during travel of the at least one vehicle on the traffic surface and directionally guiding the vehicle in relation to information gained by the optical sensing device when monitoring the passive track.
Such passive track systems are generally employed for guiding conveyance devices or objects along a control line or guide marker and to optimally exploit the flexibility of trackless conveyance equipment, as for example in the construction and operation of flexible production or manufacturing systems.
The present state of the art for the guidance of robotic transport devices is characterized by the widespread usage of electrically insulated inductive loops laid into the floor or traffic surface through which a low frequency alternating current is conducted. The laying of such inductive loops in the floor is expensive and time-consuming and the flexibility inherent in trackless vehicles is thereby under-utilized, since this type of guidance line built into the floor cannot readily have its path altered, nor can it be changed without interrupting traffic or disturbing the environment. Guidance systems have therefore become known which use passive control lines or guide markers, i.e. control or guide marker lines through which no electrical current flows. Such passive control or guide marker lines are applied directly to the floor or traffic surface without requiring electrical insulation so that they also can be easily and quickly removed at any time.
The present invention concerns a vehicle guidance system with a passive control line or guide marker, such as that described in the German Patent Publication No. 2,959,204. This known passive track guidance system functions according to the principle of brightness equilibrium and uses as a control line or guide marker a light-colored band or stripe which is bordered on both sides by two contrast-enhancing dark-colored bands or stripes. Light emitted from the vehicle is reflected from the three bands or stripes and received by two vehicle-supported light sensors, each of which generates a signal which is proportional to the average brightness within an associated window of equally large sensing or detection windows. If the first light sensor delivers a greater signal through its associated sensing window than the second light sensor through its associated sensing window, then the lateral track position of the vehicle is corrected in reference to the one light-colored and the two dark-colored bands or stripes such that both sensing windows receive the same average brightness and such that brightness equilibrium is reestablished.
As simple as this track guidance system is, it is encumbered with a number of disadvantages: For one thing, the sensitivity of the system is a function of contrast and in general is proportional to (R1-R2)/(R2+R2) with R1 and R2 equal to the respective coefficients of reflection of the light-colored and dark-colored bands or stripes. For this reason as high and especially as constant a contrast as possible must be guaranteed at the track edges in order to avoid stability problems in the steering-regulation circuit. It is therefore not possible to dispense with the two dark-colored lateral bands or stripes provided on both sides of the light-colored band or stripe. This increases the expense of a thus-designed passive track and complicates its implementation in a travel network.
Further disadvantages ensue from the fact that this track guidance system reacts exceptionally sensitively to contamination, on the one hand due to the attendant reduction in contrast and on the other hand due to the integral detection of an average brightness value as opposed to edge-tracking. In particular, the asymmetrical contamination values which must generally be expected lead directly to an indeterminate offset. It is also a disadvantage that the track guidance system according to the aforesaid German Patent Publication responds stably only as long as both detection windows have their outer edges within the dark-colored bands or stripes and their inner edges within the light-colored band or stripe. Outside this detection range an undifferentiated or passive behavior or even an inversely coupled behavior can be observed. A reduced recovery or correction zone of track guidance ensues which can have a detrimental effect upon reliability of guidance.